Climate change is set to have a dramatic impact on where malaria is prevalent, with current hotspots improving but new areas affected, a study has revealed.
Hotter and drier temperatures will lead to a reduction in mosquito breeding grounds in Africa, while areas currently unaffected, such as southern Europe, will become susceptible.
Researchers have studied the impact of rainfall and water flows, which have caused flooding and led to the creation of surface water suitable for breeding mosquitoes, which transmit malaria.
The study, entitled Future Malaria Environmental Suitability in Africa is Sensitive to Hydrology and funded by the Natural Environment Research Council, reveals climate change has already caused a four-fold increase in mosquito-friendly hotspots and created conditions for breeding grounds in places near rivers, such as the Nile, which have been malaria-free for the past few decades.
Using the new hydrology-driven model for predicting the effects of climate change on malaria transmission will mean more targeted interventions to control the disease can be used in at-risk areas.
Dr Mark Smith, an associate professor in water research at the School of Geography in Leeds, England, and lead author of the study, has been working in the field of malaria research for 15 years in Tanzania and Zambia.
He told The National the research will enable health agencies to identify mosquito-friendly areas and which interventions to use.
“This will give us a more physically realistic estimate of where in Africa is going to become better or worse for malaria,” he said.
“As increasingly detailed estimates of water flows become available, we can use this understanding to direct prioritisation and tailoring of malaria interventions in a more targeted and informed way. This is really useful given the scarce health resources that are often available.
“Our model says even at present day there are almost four times more people living in potentially malaria endemic areas than we would have thought. In the future we expect that to change, we expect to see a decrease in the areas suitable for malaria but those areas that are suitable are still around rivers and that is where the cities are.
“Those cities are going to expand massively in population and we are going to see a huge increase in the number of people in those areas driven by population growth.”
Malaria is a climate-sensitive, vector-borne disease that caused 608,000 deaths among 249 million cases in 2022.
Dr Smith said the research found the number of months suitable for transmission is set to increase.
He said the work has also highlighted the role of waterways such as the Zambezi river and the Nile in the spread of the disease.
“We expect to see southern Europe increasing in suitability for malaria,” he said.
“We have looked at the length of transmission seasons, the number of continuous months suitable for transmission and we are seeing a likely increase in areas like southern Europe. We are also seeing locally acquired cases in the US, in Florida and Texas.”
Last year, scientists at Abu Dhabi's Forecasting Healthy Futures summit revealed malaria was re-emerging in countries such as Greece where it had been previously eradicated and there had been localised outbreaks in Europe and Japan.
In the report published on Wednesday, the researchers predict that the hot and dry conditions brought about by climate change in Africa, where 95 per cent of the world’s cases are reported, will lead to an overall decrease in areas suitable for malaria transmission from 2025.
The new hydrology-driven approach also shows that changes in malaria suitability are seen in different places and are more sensitive to future greenhouse gas emissions than previously thought.
It also found that projected increases in areas such as South Africa are now seen to follow watercourses such as the Orange river.
Dr Smith said while it was positive news for the impact of malaria on Africa, climate change will bring new problems.
“What we are seeing on balance is a decrease in suitable areas in Africa but when it is too hot or too dry for the malaria parasite you are in all kinds of trouble for other things like agriculture and water availability, even dengue,” he said.
“As malaria decreases you see a swing towards dengue. It is quite a scary future when it is too hot and dry for malaria.”
Previous models have used rainfall totals to indicate the presence of surface water suitable for mosquitoes breeding, but the research led by the University of Leeds used several climatic and hydrological models to include real-world processes of evaporation, infiltration and flow through rivers.
“The key advancement is that these models factor in that not all water stays where it rains, and this means breeding conditions suitable for malaria mosquitoes too can be more widespread – especially along major river floodplains in the arid, savannah regions typical of many regions in Africa," said co-author of the study Prof Chris Thomas, of the University of Lincoln.
“What is surprising in the new modelling is the sensitivity of season length to climate change. This can have dramatic effects on the amount of disease transmitted.”
Simon Gosling, professor of climate risks and environmental modelling at the University of Nottingham, co-wrote the study and helped to co-ordinate the water modelling experiments. “Our study highlights the complex way that surface water flows change the risk of malaria transmission across Africa, made possible thanks to a major research programme conducted by the global hydrological modelling community to compile and make available estimates of climate change impacts on water flows across the planet," he said.
“Although an overall reduction in future risk of malaria might sound like good news, it comes at a cost of reduced water availability and a greater risk of another significant disease, dengue.”
The researchers hope further advances in their modelling will allow for even finer details of waterbody dynamics which could help to inform national malaria control strategies.
“We're getting to the point soon where we use globally available data to not only say where the possible habitats are, but also which species of mosquitoes are likely to breed where," Dr Smith said.
"This will allow people to really target their interventions against these insects.”
